Wastewater treatment method

Abstract

To provide a wastewater treatment method for separating wastewater containing oil, suspended solid and / or oil-bound suspended solid into water, oil to be floated, and suspended solid with low oil content.SOLUTION: There is provided a wastewater treatment method for reducing the concentrations of oil and suspended solid in wastewater containing the oil and the suspended solid and / or oil-bound suspended solid, the method including an oil separation agent adding step for adding an oil separation agent so that the oil separation agent is included in at least one location of the step where the oil and / or the suspended solid occurs and the step of having the wastewater containing the oil, the suspended solid and / or the oil-bound suspended solid. The oil separation agent contains a nonionic polymer compound as an active component.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a wastewater treatment method for reducing the oil concentration and suspended solid concentration in wastewater.

Background Art

[0002] In processing and refining factories such as silicon manufacturing and processing factories, ceramic manufacturing and processing factories, metal manufacturing and processing factories, and metal refining factories, water and cutting oil, lubricating oil, etc. are frequently used in cutting processes and manufacturing processes. In addition, in these processing and refining factories, process water and wastewater containing oil and dust generated in the cutting process and manufacturing process (for example, dust mixed with coal dust, ore dust, inorganic compound powder, and metal powder alone or in multiple types) are generated. Therefore, in these facilities, the water treatment of process water and wastewater containing dust with oil attached or combined (suspended substances with oil attached or combined in water) and oil, etc. often becomes a technical problem during disposal or recycling. To solve such technical problems, it is necessary to separate and float the oil in the process water and wastewater and the oil attached or combined to the suspended particles, and sediment the suspended particles, so as to separate them into clear water, the oil separated in a floating form, and suspended substances with a low oil content rate.

[0003] Generally, wastewater and process water containing oil and dust with oil attached or combined (suspended substances with oil attached or combined in water) are treated with inorganic chemicals containing aluminum or iron and polymer flocculants, and are separated by sedimentation or floating in a thickener or a dissolved air flotation device as sludge. In addition, although the suspended substances in process water and wastewater are often combined with oil to form oily sludge, it is difficult to separate the suspended substances combined with oil into oil and suspended substances. Therefore, generally, it is treated by sedimentation separation or floatation separation as oily sludge.

[0004] In addition, in a metal manufacturing process such as a steelworks, there are processes for casting molten iron and rolling hot semi-finished products, and water for cooling circulates. After this cooling water is sprayed onto the high-temperature steel material, it is collected in the lower trough and sent to a scale pit or a cross-flow sedimentation tank, where it is treated with an organic flocculant or an inorganic flocculant. The treated water obtained is reused directly as cooling water after cooling. In Patent Documents 1 to 5, as such wastewater treatment for a direct cooling water system, coarse suspended substances (coarse SS) such as metal powder and oil content with a particle size of 50 μm or more and fine suspended substances (fine SS) with a particle size less than 50 μm contained in the direct cooling water are coagulated, flocculated, and sedimented in the same treatment using a coagulant / sedimentation agent mainly composed of a cationic or amphoteric copolymer, and removed simultaneously. In these treatment methods for direct cooling water, a specific polymer (the above coagulant / sedimentation agent) is added to wastewater containing coarse SS and fine SS, and the suspended substances containing oil are coagulated, flocculated, and sedimented in the scale pit, and the suspended substances containing oil and the like are removed from the water to obtain clarified treated water.

[0005] When using the treatment method of coagulating, flocculating, and sedimenting coarse SS and fine SS containing oil and the like in the same treatment, the sludge accumulated in the scale pit contains oil. Here, scales without oil content are useful resources that are reused in the manufacturing process and the like. Therefore, when the sludge accumulated in the scale pit contains oil, it is necessary to separate the oil in order to reuse the sludge.

[0006] As a method for separating oil from oil-containing sludge, for example, there is a method of extracting oil from the oil-containing sludge into an organic solvent by mixing an organic solvent as an extractant with the oil-containing sludge and vigorously stirring it (see Patent Document 6). However, since the oil-containing sludge contains moisture, a stabilized emulsion is formed in such a treatment. To break (demulsify) such a stabilized emulsion, a multi-disc type centrifuge is required, and there is a problem that the equipment investment cost increases (see Patent Documents 7 and 8).

[0007] Furthermore, the oily sludge is temporarily stored in tanks such as sedimentation tanks and thickening tanks at steelworks, and is transported to a treatment facility when it is being treated for disposal or when it is being treated for use as a steelmaking raw material. However, since the oily sludge has a high water content and many of them are easy to flow, there is a concern that the oily sludge and the oil content contained in the oily sludge will flow out during transportation. Therefore, the oily sludge is subject to restrictions on the amount of transportation and drying during transportation, as compared with sludge that can be directly used as a steelmaking raw material, such as sludge that does not contain oil. Therefore, it is also necessary to make the oily sludge into a form that is easy to transport (Patent Document 9).

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Patent Document 9

Summary of the Invention

Problems to be Solved by the Invention

[0009] As described above, the water (process water and wastewater) handled in processing and refining factories such as silicon manufacturing and processing factories, ceramics manufacturing and processing factories, metal manufacturing and processing factories, and metal refining factories contains oil and dust generated during cutting and manufacturing processes (for example, dust mixed with coal dust, ore dust, inorganic compound powder, and metal powder alone or in multiple types). In water, the oil and the above-mentioned dust (suspended substances in water) exist in a state of separation and / or combination. If such wastewater containing oil, suspended substances, and / or oil-bound suspended substances can be separated into clean water, floating-separated oil, and suspended substances with a low oil content, an effective wastewater treatment method can be realized. In addition, in equipment that reuses such wastewater containing oil, suspended substances, and / or oil-bound substances as cooling water, an especially effective wastewater treatment method can be realized.

[0010] Furthermore, according to the above water treatment method, since the oil content in the suspended substances obtained after treatment is low, the industrial waste discarded as oil-containing sludge is reduced, and the equipment load and treatment cost imposed on the oil-containing wastewater treatment equipment can be significantly reduced. And when the oil content of the recovered suspended substances (also referred to as sediment sludge and settling sludge) is reduced, the sediment sludge can be recycled as a raw material or the like. Furthermore, at the same time, the floating oil recovered can also be reused as fuel.

[0011] In many factories, wastewater and process water containing oil and suspended substances are rarely reused. However, in special metal manufacturing processes such as steel mills, there are processes for casting molten iron and rolling hot semi-finished products, and water for cooling circulates. These direct system circulating cooling waters are sprayed onto high-temperature steel materials, collected in the lower troughs, and sent to scale pits and cross-flow sedimentation basins, where they are treated through filtration facilities and cooling towers. However, with conventional treatment methods, it is difficult to separate inorganic compounds, metals, or metal oxide particles when they bind to oil, and the development of an effective separation method is desired. Also, according to conventional treatment methods, oil often remains in the recycled water, causing problems with COD in wastewater treatment. Therefore, separation of inorganic compounds and the like from oil and reduction of oil content in the treated water are required.

[0012] An object of the present invention is to provide a wastewater treatment method for separating wastewater containing oil, suspended substances, and / or oil-bound suspended substances into water, oil separated by floatation, and suspended substances with a low oil content. Another object of the present invention is to provide a method for reusing wastewater containing oil, suspended substances, and / or oil-bound suspended substances, a method for reusing oil and / or suspended substances in wastewater containing oil, suspended substances, and / or oil-bound suspended substances. Also, an object of the present invention is to provide an oil separation agent used for wastewater containing oil, suspended substances, and / or oil-bound suspended substances.

Means for Solving the Problems

[0013] As a result of intensive studies to solve the above problems, the present inventors have found that in order to treat wastewater containing oil, suspended substances, and / or oil-bound suspended substances, by adding a specific oil separation agent (i.e., a nonionic polymer compound) so that the oil separation agent is included in at least one of the process where oil and / or suspended substances are generated and the process having wastewater containing oil, suspended substances, and / or oil-bound suspended substances, the oil concentration and suspended substance concentration in the wastewater can be effectively reduced, and thus the present invention has been completed.

[0014] That is, the present invention is a wastewater treatment method for reducing the oil concentration and the suspended solid concentration in wastewater containing oil, suspended solids, and / or oil-bound suspended solids, wherein the oil and / or the suspended solids are generated in a process, and an oil separation agent is added such that the oil separation agent is included in at least one of the process where the oil, the suspended solids, and / or the oil-bound suspended solids are generated and the process where wastewater containing the oil, the suspended solids, and / or the oil-bound suspended solids is present. The oil separation agent contains a nonionic polymer compound as an active ingredient, and is characterized by being a wastewater treatment method. In the oil separation agent addition step, the oil separation agent is added to at least one of the process where the oil and / or the suspended solids are generated and the supply water supplied to the process where wastewater containing the oil, the suspended solids, and / or the oil-bound suspended solids is present. The oil concentration of the supply water is preferably 5 ppm or less, and the suspended solid concentration is preferably 20 ppm or less. The wastewater treatment method of the present invention is preferably used in a direct cooling water system in a continuous casting facility or a rolling facility in the iron and steel industry. It is preferable to use the treated water obtained from the wastewater treatment method of the present invention as the supply water. The wastewater treatment method of the present invention is preferably used for reusing the oil and / or suspended solids separated from the wastewater.

[0015] Further, the present invention is also an oil separation agent used for wastewater containing oil, suspended solids, and / or oil-bound suspended solids, and is characterized by containing a nonionic polymer compound as an active ingredient. The nonionic polymer compound is preferably a homopolymer, copolymer, or terpolymer containing at least one monomer selected from the group consisting of acrylamide, ethylene oxide, propylene oxide, methyl vinyl ether, vinyl alcohol, and vinyl acetamide as a constituent component.

Effects of the Invention

[0016] According to the present invention, it is possible to provide a wastewater treatment method for separating wastewater containing oil, suspended substances, and / or oil-bound suspended substances into water, oil separated by floatation, and suspended substances with a low oil content. Also according to the present invention, it is possible to provide a method for reusing wastewater containing oil, suspended substances, and / or oil-bound suspended substances, and a method for reusing oil and / or suspended substances in wastewater containing oil, suspended substances, and / or oil-bound suspended substances. Furthermore, according to the present invention, it is possible to provide an oil separation agent for use in wastewater containing oil, suspended substances, and / or oil-bound suspended substances.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0018] Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following description.

[0019] The present invention is a wastewater treatment method for reducing the oil concentration and suspended substance concentration in wastewater containing oil, suspended substances, and / or oil-bound suspended substances, wherein the oil and / or the suspended substances are generated in a process, and an oil separation agent is added so that the oil separation agent is included in at least one of the processes having wastewater containing the oil, the suspended substances, and / or the oil-bound suspended substances. The oil separation agent contains a nonionic polymer compound as an active ingredient.

[0020] The inventors of the present invention studied the above-mentioned problems of the prior art, and without causing an increase in equipment investment costs and the like, in an easy way and more effectively, wastewater containing oil, suspended substances, and / or oil-bound suspended substances is separated into water, oil separated by floating, and suspended substances with a low oil content. The inventors studied wastewater treatment methods. And in order to achieve this problem, it was found that the following three technologies are important. The first is a technology for floating and separating oil in wastewater, the second is a technology for sedimentation separation of suspended substances in wastewater, and the third is a technology for separating oil-bound suspended substances (oil-containing sludge) into oil and suspended substances. Regarding the above-mentioned first and second technologies, conventionally, it has been shown that oil separation agents, coagulants, and flocculants made of organic compounds are effective for floating separation of oil and sedimentation separation of suspended substances. However, a technology that can obtain a sufficient floating separation effect of oil and a sufficient sedimentation separation effect of suspended substances using the same oil separation agent has not been disclosed. Conventionally, cationic polymer compounds and amphoteric polymer compounds of cationic anions have been used for floating separation of oil and sedimentation separation of suspended substances in wastewater. However, simply adding these agents to wastewater only results in the action of sedimenting oil, suspended substances, and / or oil-bound suspended substances in wastewater together, but the floating separation effect of oil and the sedimentation separation effect of suspended substances cannot be obtained sufficiently. That is, with the conventionally used cationic polymer compounds and amphoteric polymer compounds of cationic anions, wastewater containing oil, suspended substances, and / or oil-bound suspended substances cannot be separated into water, oil separated by floating, and suspended substances with a low oil content. And for the third technology of separating oil-bound suspended substances (oil-containing sludge) into oil and suspended substances, no inexpensive and practical solution has been proposed. In order to solve these problems, the inventors further studied and found that by adding an oil separation agent containing a nonionic polymer compound as an active ingredient to at least one of the steps where oil and / or suspended substances are generated and the steps where wastewater containing oil, suspended substances and / or oil-bound suspended substances is present, an excellent floating separation effect of oil and sedimentation separation effect of suspended substances can be obtained, thus completing the present invention.

[0021] According to the wastewater treatment method of the present invention, there is an oil separation agent addition step of adding an oil separation agent so that the oil separation agent is contained in at least one of the steps where oil and / or suspended substances are generated and the steps where wastewater containing oil, suspended substances and / or oil-bound suspended substances is present. Since the above oil separation agent contains a nonionic polymer compound as an active ingredient, the oil-bound suspended substances in the wastewater are separated into oil and suspended substances, the oil in the wastewater is separated by floating, and the suspended substances in the wastewater are separated by sedimentation. Thereby, wastewater containing oil, suspended substances and / or oil-bound suspended substances can be separated into water, oil separated by floating, and suspended substances with a low oil content.

[0022] Further, the present invention is also an oil separation agent used for wastewater containing oil, suspended substances and / or oil-bound suspended substances, characterized in that it contains a nonionic polymer compound as an active ingredient. As described above, by treating wastewater containing oil, suspended substances and / or oil-bound suspended substances with the oil separation agent of the present invention, it can be separated into water, oil separated by floating, and suspended substances with a low oil content.

[0023] In the oil separation agent addition step in the wastewater treatment method of the present invention, it is preferable to add the oil separation agent to at least one of the supply water supplied to the steps where oil and / or suspended substances are generated and the steps where wastewater containing oil, suspended substances and / or oil-bound suspended substances is present. It is preferable that the oil concentration of the above supply water is 5 ppm or less and the suspended substance concentration is 20 ppm or less. A specific oil separator is added to clarified supply water with an oil concentration of 5 ppm or less and a suspended solid concentration of 20 ppm or less, which is supplied to at least one of a process where oil and / or suspended substances are generated and a process having wastewater containing the oil, the suspended substances, and / or the oil-bound suspended substances, thereby preventing the adhesion or binding of the oil to the suspended substances. Therefore, regarding the technology for separating the above-mentioned third oil-bound suspended substance (oil-containing sludge) into oil and suspended substances, by preventing the adhesion or binding of the oil and the suspended substances in the wastewater to form an oil-bound suspended substance, the generation of oil-bound suspended substances that are difficult to separate is suppressed, and by maintaining the separation state of the oil and the suspended substances in the wastewater, the wastewater containing the oil, the suspended substances, and / or the oil-bound suspended substances can be separated more highly into water, the oil separated by floatation, and the suspended substances with a low oil content rate.

[0024] The oil separator in the present invention may contain a nonionic polymer compound as an active ingredient. As the nonionic polymer compound, in addition to a complete nonionic polymer compound that does not exhibit ionicity, among the constituent components of the polymer compound, a weakly ionic (cationic or anionic) polymer compound with a molar ratio of monomers exhibiting ionicity (cationic or anionic) of 5% or less is also included. Examples of the nonionic polymer compound used in the present invention include homopolymers, copolymers, and terpolymers synthesized from monomers such as acrylamide, ethylene oxide, propylene oxide, methyl vinyl ether, vinyl alcohol, and vinyl acetamide, weakly anionic copolymers and terpolymers in which the molar ratio of anionic monomers such as acrylic acid is less than 5%, and weakly cationic copolymers and terpolymers in which the molar ratio of cationic monomers such as dimethylaminoethyl methacrylate is less than 5%. The nonionic polymer compound used in the present invention is a homopolymer, copolymer, and / or terpolymer containing at least one monomer selected from the group consisting of acrylamide, ethylene oxide, propylene oxide, methyl vinyl ether, vinyl alcohol, and vinyl acetamide as a constituent component, a weakly anionic copolymer and / or terpolymer in which the molar ratio of anionic monomers such as acrylic acid is less than 5%, and a weakly cationic copolymer and / or terpolymer in which the molar ratio of cationic monomers such as dimethylaminoethyl methacrylate is less than 5%, and is preferably one or more of these. Further, as the nonionic polymer compound used in the present invention, at least one selected from the group consisting of a polymer of acrylamide, a copolymer and / or terpolymer having a structure containing acrylamide as a constituent component as a monomer and containing one or more monomers selected from ethylene oxide, propylene oxide, methyl vinyl ether, vinyl alcohol, and vinyl acetamide as constituent components, and a weakly anionic copolymer and / or terpolymer in which the molar ratio of anionic monomers such as acrylic acid is less than 5% is more preferable. In addition, the oil separator in the present invention preferably contains, as an active ingredient, a completely nonionic polymer compound that does not exhibit ionic properties and / or a weakly anionic polymer compound in which the molar ratio of monomers exhibiting anionic properties among the constituent components of the polymer compound is less than 5%, and more preferably contains a completely nonionic polymer compound that does not exhibit ionic properties.

[0025] In addition, the weight average molecular weight of the homopolymer, copolymer or terpolymer, which is a nonionic polymer compound in the present invention, is preferably from 3 million to 20 million. If the weight average molecular weight is too small compared to the above range, the polymerization reaction is difficult to control and synthesis is difficult, and a sufficient sedimentation separation effect of the suspended substance cannot be obtained. On the other hand, if it is too large, its viscosity increases and it may be difficult to use. The weight average molecular weight of the homopolymer, copolymer or terpolymer, which is a nonionic polymer compound synthesized from the above monomers, is more preferably from 6 million to 17 million.

[0026] The addition amount of the oil separating agent in the wastewater treatment method of the present invention may be determined according to the amount and concentration of the oil and suspended substances in the wastewater, but it is preferably added in the range of 0.05 to 5 ppm, and more preferably added in the range of 0.5 to 3 ppm.

[0027] The wastewater treatment method of the present invention only needs to have an oil separating agent addition step of adding the above oil separating agent so that the above oil separating agent is contained in at least one of the step where oil and / or suspended substances are generated and the step having wastewater containing oil, suspended substances and / or oil-bound suspended substances. The addition position and addition method of the oil separating agent are not particularly limited. Further, in the wastewater treatment method of the present invention, the oil separation agent is supplied to at least one location of the supply water in the process where oil and / or suspended substances are generated, and in the process having wastewater containing oil, suspended substances and / or oil-bound suspended substances. It is preferably added to clear supply water with an oil concentration of 5 ppm or less and a suspended substance concentration of 20 ppm or less. In this case, whether or not the oil separation agent is added to the wastewater after oil and / or suspended substances are mixed into the supply water (also expressed as direct water in which oil and / or suspended substances are mixed, hereinafter simply referred to as direct water) is not particularly limited. Note that, from the viewpoint of suppressing the usage amount of the oil separation agent and expecting a higher separation effect, the wastewater treatment method of the present invention is used in the process where oil and / or suspended substances are generated, and in the process having wastewater containing oil, suspended substances and / or oil-bound suspended substances. It is more preferable that the oil separation agent is added only to clear supply water with an oil concentration of 5 ppm or less and a suspended substance concentration of 20 ppm or less at at least one location of the supply water supplied to the process.

[0028] In addition, in the wastewater treatment method of the present invention, within the range where the effects of the present invention are achieved, other chemicals may be used in addition to the above oil separation agent. Examples of other chemicals include anionic polymers and inorganic coagulants such as polyaluminum chloride and iron sulfate. These inorganic coagulants may be added so as to be included in at least one of the process where oil and / or suspended substances are generated and the process having wastewater containing the oil, the suspended substances and / or the oil-bound suspended substances. These inorganic coagulants may be added, for example, to at least one location of the supply water supplied to the process where oil and / or suspended substances are generated and the process having wastewater containing the oil, the suspended substances and / or the oil-bound suspended substances, to supply water with an oil concentration of 5 ppm or less and a suspended substance concentration of 20 ppm or less (hereinafter also simply referred to as clear supply water), or may be added to the wastewater (direct water) after oil and / or suspended substances are mixed in. However, from the viewpoint of suppressing the usage amount of the chemical and expecting a higher separation effect, it is more preferable that other chemicals are added only to the above clear supply water with an oil concentration of 5 ppm or less and a suspended substance concentration of 20 ppm or less.

[0029] In the wastewater treatment method of the present invention, when the oil separator is added to at least one location of the feed water supplied to a process where oil and / or suspended substances are generated and a process having wastewater containing oil, suspended substances, and / or oil-bound suspended substances, the oil concentration of the feed water is preferably 5 ppm or less, more preferably 3 ppm or less. Also, the suspended substance concentration of the feed water is preferably 20 ppm or less, more preferably 10 ppm or less. As a position where the oil separator is added to such feed water (clarified feed water), for example, chemical injection positions shown in FIGS. 1 and 2 can be mentioned. By adding the oil separator to the clarified feed water at the chemical injection positions shown in FIGS. 1 and 2, adhesion or binding between oil and suspended substances generated in downstream processes can be prevented, generation of oil-bound suspended substances can be suppressed, and oil and suspended substances in the wastewater can be maintained in a separated state.

[0030] In the wastewater treatment method of the present invention, when the oil separator is added to at least one location of the feed water supplied to a process where oil and / or suspended substances are generated and a process having wastewater containing the oil, the suspended substances, and / or the oil-bound suspended substances, it is preferable that the oil separator is added at a position where the feed water (clarified feed water) with an oil concentration of 5 ppm or less (preferably 3 ppm or less) and a suspended substance concentration of 20 ppm or less (preferably 10 ppm or less) is efficiently dispersed and mixed before being supplied into the plant. For example, using a chemical injection nozzle of a type that mixes chemicals together with a chemical injection quill or pressurized water in the feed water line of the clarified feed water supplied to the plant or in the feed water line of the clarified feed water supplied to the scale-through or spray, the method of injecting the oil separator, or using a chemical dilution and mixing line including a mixer and injecting the oil separator, is preferable in that the oil separator is sufficiently mixed in the feed water and the effects of the present invention are more effectively exerted. Therefore, the oil separator is preferably added using a chemical injection nozzle of a type that mixes chemicals together with a chemical injection quill or pressurized water, and is preferably added to a mixing line including a mixer among the feed water lines.

[0031] In the wastewater treatment method of the present invention, the quality of the supply water is such that the oil concentration is 5 ppm or less and the suspended solid concentration is 20 ppm or less. The oil concentration and the suspended solid concentration can be measured using ordinary methods in the field to which the present invention pertains and are not particularly limited. For example, the oil concentration can be measured by the N-hexane extract measurement method based on JIS K 0101 or JIS K 0102, and the suspended solid concentration can be measured by methods such as the GFP filtration gravimetric method or the MF filtration gravimetric method. In the wastewater treatment method of the present invention, it is preferable that the oil concentration of the supply water is 3 ppm or less, and it is preferable that the suspended solid concentration is 10 ppm or less.

[0032] In many factories, oily wastewater and oily process water containing oil and suspended solids are rarely reused. However, in special metal manufacturing processes such as steel mills, there are processes of casting molten iron and rolling hot semi-finished products, and the spray water for cooling circulates. Note that FIG. 1 is a schematic diagram showing a preferred example when the wastewater treatment method of the present invention is applied to the direct cooling water system of a continuous casting process. Also, FIG. 2 is a schematic diagram showing a preferred example when the wastewater treatment method of the present invention is applied to the direct cooling water system of a rolling process. In these processes, cooling water is sprayed onto hot intermediate products or steel materials, and the cooling water containing oil, suspended solids, and / or oil-bound suspended solids is collected in the lower trough (scale-through trough) and sent to a scale pit or a cross-flow sedimentation pond. After being treated through filtration equipment and a cooling tower, it is reused as cooling water again. According to the wastewater treatment method of the present invention, wastewater containing oil, suspended solids, and / or oil-bound suspended solids can be effectively separated into water, oil separated by floatation, and suspended solids with a low oil content. Therefore, it can be suitably used for the treatment of the direct cooling water system of such continuous casting equipment or rolling equipment.

[0033] Moreover, according to the wastewater treatment method of the present invention, the oil-bound suspended substances in the wastewater are separated into oil and suspended substances, and further, the adhesion or binding between the oil and the suspended substances in the wastewater is suppressed, and the oil and the suspended substances are maintained in a separated state in the wastewater. Therefore, in the above scale pit and cross-flow sedimentation tank, efficient floating separation of oil and sedimentation separation of suspended substances are achieved. Therefore, the oil concentration and suspended substance concentration in the treated water obtained from the wastewater treatment method of the present invention are low, and the treatment load in subsequent filtration equipment and cooling towers can be significantly reduced. Furthermore, sufficient effects such as improvement of operation efficiency due to reduction of pipe blockage and dirt, and reduction of operation cost and improvement of operation efficiency due to reduction of load on water treatment equipment such as filters and cross-flow sedimentation are obtained. Therefore, the wastewater treatment method of the present invention is preferably used in the direct cooling water system in the continuous casting equipment and / or rolling equipment in the iron and steel industry. Moreover, the wastewater treatment method of the present invention is preferably used for reducing equipment load.

[0034] Moreover, according to the wastewater treatment method of the present invention, since treated water with low oil concentration and suspended substance concentration can be obtained, the obtained treated water is preferably reused as supply water again. When the wastewater treatment method of the present invention reuses the treated water obtained by the wastewater treatment method, the oil concentration in the treated water is 5 ppm or less and the suspended substance concentration is 20 ppm or less, but preferably the oil concentration in the treated water is 3 ppm or less and the suspended substance concentration is 10 ppm or less.

[0035] The wastewater treatment method of the present invention includes a step of generating oil and / or suspended substances, and a step of adding an oil separation agent to at least one location of the supply water supplied to a step having wastewater (direct water) containing the oil, the suspended substances, and / or the oil-bound suspended substances. This configuration can be rephrased as a step of adding an oil separation agent to at least one of the supply line for supplying water to the step where oil and / or suspended substances are generated, and the supply line for supplying water to the step having wastewater containing oil, suspended substances, and / or oil-bound suspended substances. Further, when using the treated water obtained by the wastewater treatment method of the present invention as the supply water, the above supply line can be rephrased as a supply line for supplying the treated water. In this specification, the supply water and the treated water transported in the supply line where the oil separation agent is added are supply water or treated water with an oil concentration of 5 ppm or less and a suspended substance concentration of 20 ppm or less.

[0036] Also, according to the wastewater treatment method of the present invention, wastewater containing oil, suspended substances, and / or oil-bound suspended substances can be effectively separated into water, oil separated by floating, and suspended substances with a low oil content. Therefore, the water (treated water), oil separated by floating, and suspended substances with a low oil content obtained by the wastewater treatment method of the present invention are preferably reused as supply water, raw materials, or fuel again. Further, the wastewater treatment method of the present invention is preferably used for reusing the oil and / or suspended substances separated from the wastewater. The suspended substances with a low oil content can be reused as raw materials for each factory and can also be used in other factories as recycled raw materials.

[0037] As one aspect, the present invention is a method for reusing oil and / or suspended substances in wastewater containing oil, suspended substances, and / or oil-bound suspended substances, including a step of generating the oil and / or the suspended substances, and a step of adding an oil separation agent so that the oil separation agent is included in at least one of the steps having wastewater containing the oil, the suspended substances, and / or the oil-bound suspended substances. The oil separation agent addition step of adding the oil separation agent, and the oil separation agent is a nonionic polymer compound. It may be a reuse method characterized by this. When the present invention is a reuse method, the description regarding a preferred embodiment of the oil separator used, a preferred addition position and addition method of the oil separator, a method for measuring the quality of the feed water, and other chemicals used is the same as that in the wastewater treatment method of the present invention described above.

[0038] According to the wastewater treatment method and the reuse method of the present invention, wastewater containing oil, suspended substances and / or oil-bound suspended substances can be effectively separated into water, oil separated by floatation, and suspended substances with a low oil content. In the present invention, the suspended substances with a low oil content (also referred to as oil content) are suspended substances with an oil content of 1% or less. The oil content in the suspended substances is a weight ratio and can be measured based on JIS K0101 or JIS K0102 as normal hexane extract. Note that the sedimented suspended substances in the wastewater are called sludge. According to the wastewater treatment method and the reuse method of the present invention, since the oil content of the sludge can be reduced, the sludge obtained by the wastewater treatment method and the reuse method of the present invention can be reused. The oil content of the sludge obtained by the wastewater treatment method and the reuse method of the present invention is preferably 3% or less, and more preferably 1.5% or less.

[0039] FIG. 1 is a schematic diagram showing a preferred example of applying the wastewater treatment method of the present invention to the direct cooling water system of a continuous casting process. As shown in FIG. 1, the supply water supplied to the continuous casting apparatus 1 and / or the scale through-pass 2 moves to the scale pit 3 while flowing inside the scale through-pass 2. In the example shown in FIG. 1, an oil separator (chemical) is added at at least one of the supply water supplied to the continuous casting apparatus 1 and the scale through-pass 2 and the scale through-pass 2. By adding the oil separator in this way so as to be included in at least one of the process in which oil and / or suspended substances are generated in the continuous casting apparatus 1 and the process having wastewater containing oil, suspended substances and / or oil-bound suspended substances, the adhesion or binding of oil and suspended substances in the wastewater is suppressed in the scale through-pass 2, and the oil and suspended substances in the wastewater are separated and sent to the scale pit 3. When the oil separator is added to the supply water supplied to the scale through-pass 2, the oil separator is stirred and mixed by a pump or piping in the path when the supply water is supplied to the scale through-pass 2, and is supplied to the scale through-pass 2 in a state of being sufficiently diffused in the supply water. Thereby, the adhesion or binding of oil and suspended substances in the wastewater is suppressed in the scale through-pass 2, and the oil and suspended substances in the wastewater are separated and sent to the scale pit 3. In the scale pit 3, the condensed and aggregated oil and suspended substances in the wastewater are separated extremely quickly, the oil is separated by floating, and the suspended substances are separated by sedimentation. Therefore, the intermediate layer in the scale pit 3 becomes clear treated water. Note that the treated water may be further sent to a cross-flow sedimentation tank 4 to further separate oil and suspended substances. The treated water is supplied to the plant again as direct cooling water through a filter 5 and a cooling tower 6. When the oil separator is added to the supply water in the continuous casting apparatus 1, the oil separator is stirred and mixed by a nozzle when the supply water is supplied, and is supplied to the continuous casting apparatus 1 in a state of being sufficiently diffused in the supply water, which is more preferable than the case of directly adding it to the scale through-pass 2. FIG. 2 is a schematic diagram showing a preferred example of applying the wastewater treatment method of the present invention to the direct cooling water system of a rolling process. The description in FIG. 1 above can be used as the description of FIG. 2 by replacing the continuous casting apparatus 1 in FIG. 1 with the rolling equipment 7 in FIG. 2.

Example

[0040] Hereinafter, the present invention will be further described with reference to examples. However, the present invention is not limited to the following examples.

[0041] <Drug Confirmation Test> (Examples 1 and 2, and Comparative Examples 1 and 2) In order to confirm the effects of the present invention, a drug effect confirmation test was conducted when the injection order using a glass bottle was changed. The test procedure was as follows: For each test, three 500-ml glass bottles containing 300 ml of clear water (Osaka City tap water) were prepared. To these, the chemicals (nonionic polymer oil separator) (2 ppm) shown in Table 1, a mixture (1 g) of fine particles of iron and iron oxide with a size of 100 μm or less as suspended substances, and lubricating oil (0.5 g) as oil were added in the order shown in Table 1. Then, shaking and stirring were performed for 15 seconds, and after standing for 15 minutes, the suspended substance concentration (SS (ppm)), normal hexane extractable oil content (oil content (ppm)), and turbidity (FTU) in the water were measured. When the chemicals, suspended substances, and oil were added in the order described in Table 1 below, shaking and stirring were performed for 15 seconds after adding each of the above substances, and then the next additive was added. All confirmation tests were carried out at room temperature (25°C). In addition, the oil content concentration (oil content (ppm)) of the above clear water (Osaka City tap water) was less than 1 ppm, and the suspended substance concentration (SS (ppm)) was less than 3 ppm. The oil content concentration (ppm) was measured using the N-hexane extractable substance measurement method based on JIS K 0102, the suspended substance concentration (SS (ppm)) was measured using the GFP filtration gravimetric method and the MF filtration gravimetric method, and the turbidity (FTU) was measured in accordance with JIS K0101 ("Industrial Water Test Method"). The measurement results are shown in Table 2 below. The measurement results shown in Table 2 are the average values for n = 3.

[0042] The following chemicals were used. Nonionic polymer compound: Polymer of acrylamide (weight average molecular weight: 9 million) Cationic polymer compound: Copolymer of acryloyloxyethyl compound containing acrylamide and quaternary ammonium salt (molecular weight 4.6 million)

[0043]

Table 1

[0044]

Table 2

[0045] From the results of Table 1 and Table 2 above, the suspended solid concentration (SS), normal hexane extractable oil content (oil content (ppm)), and turbidity (FTU) in Examples 1 and 2 were all sufficiently lower than the SS, oil content (ppm), and turbidity (FTU) in the water according to Comparative Example 1. Also, when comparing Examples 1 and 2 with Comparative Example 2, the suspended solid concentration (SS), normal hexane extractable oil content (oil content (ppm)), and turbidity (FTU) all showed lower values in Examples 1 and 2. Therefore, it was confirmed that the nonionic polymer compound can separate oil and suspended substances in wastewater at a higher level compared to the conventionally used cationic polymer compound. Also, when comparing Example 1 and Example 2, in Example 2 where the oil separator was added to clear water with low oil concentration and suspended solid concentration before oil and / or suspended substances were mixed in, the suspended solid concentration in water (SS (ppm)), normal hexane extractable oil content (oil content (ppm)), and turbidity (FTU) were all significantly lower. Therefore, it is considered that the binding of oil and suspended substances in water was effectively suppressed, and by maintaining the separated state of oil and suspended substances, the subsequent floating separation of oil and sedimentation separation of suspended substances were carried out promptly, effectively reducing the oil concentration and suspended solid concentration in the test wastewater.

[0046] <Confirmation test with actual machine> (Examples 3 to 4, and Comparative Example 3) A verification test was conducted on-site in the direct cooling water line of a continuous casting plant of a certain steel company. Before the evaluation test, the concentration of suspended solids (SS) and the oil content in the direct cooling water discharged from the continuous casting plant showed an upward trend, and there was a need to reuse the sludge (scale, suspended solids) sedimented in the scale pit and cross-flow sedimentation tank for cost improvement purposes. In the on-site verification test, in addition to adding the chemicals (nonionic polymer oil separator) shown in Table 3 at the addition concentrations and addition positions shown in Table 3, the water quality of the treated water at the outlet of the cross-flow sedimentation tank and the oil content of the sediment sludge in the cross-flow sedimentation tank were measured. The period during which the verification test was conducted was one month, and measurements were taken for the treated water and sediment sludge every week from the start of each test. The suspended solid concentration (SS (ppm)), oil concentration (oil (ppm)), and sediment sludge oil content ratio (%) shown in Table 4 below are the average values of the measurement results obtained from a total of four measurements starting from the start of each test. Also, the oil concentration (oil (ppm)) of the clean direct water with the chemicals added in the examples was 0.6 - 1.8, and the suspended solid concentration (SS (ppm)) was 4 - 9. The oil concentration (ppm) and the sediment sludge oil content ratio were measured using the N-hexane extract measurement method based on JIS K 0102, and the suspended solid concentration (SS) was measured using the GFP filtration gravimetry and MF filtration gravimetry, respectively. The measurement results are shown in Table 3.

[0047] The following chemicals were used. Anionic polymer compound: Sodium polyacrylate polymer (weight average molecular weight: 7 million) Nonionic polymer compound: Polymer of acrylamide (weight average molecular weight: 9 million)

[0048]

Table 3

[0049] From the results in Table 3 above, in Comparative Example 3 related to conventional wastewater treatment (addition of an anionic polymer to the inlet of the scale pit), both the SS concentration and the oil concentration in the treated water at the outlet of the cross-flow sedimentation tank were high values, and they did not meet the standards for environmental regulations and reuse in the factory. Also, in Example 3 (addition of a nonionic polymer oil separator to the scale-through sump), chemicals were added to the sump (scale-through sump) where the direct water falls at the lower part of the plant. The average values of the SS concentration (ppm) and the oil concentration (ppm) of the treated water at the outlet of the cross-flow sedimentation tank were significantly improved compared to the conventional wastewater treatment (Comparative Example 3). And the sediment sludge oil content rate (%) was also significantly improved. The effect was sufficient compared to the conventional treatment, and by adding a nonionic polymer oil separator, wastewater containing oil, suspended substances, and oil-bound suspended substances could be separated into clean water, floating-separated oil, and suspended substances with a low oil content. In Example 4, a nonionic polymer oil separator was added to the supply water (specifically, the clarified treated water in the supply water line to the spray and the scale-through sump) supplied to the process where oil and suspended substances are generated. The average values of the SS concentration (ppm), the oil concentration (ppm), and the sediment sludge oil content rate (%) of the treated water at the outlet of the cross-flow sedimentation tank were significantly lower compared to the numerical values in Comparative Example 3 and Example 3. By adding a nonionic polymer oil separator to the clean supply water, wastewater containing oil, suspended substances, and oil-bound suspended substances could be effectively separated into clean water, floating-separated oil, and suspended substances with a low oil content. Moreover, the oil content of the sediment sludge collected in the cross-flow sedimentation tank was as high as 5% or more in the treatment with the current anionic polymer in Comparative Example 3 and was not suitable for recycling. Also, in Example 3, chemicals were injected into the direct water containing the oil and suspended substances in the scale-through sump, and the oil content of the sediment sludge decreased to about 3%, meeting the factory's own recycling standards. That is, the obtained sediment sludge was recyclable as part of the raw materials. On the other hand, in Example 4 where the chemical was added to the clean treated water supply line of the spray water line, the oil content of the sediment sludge decreased to less than 1%, and the oil concentration in the sediment sludge sufficiently decreased below the recycling standard of the factory. That is, the obtained sediment sludge was recyclable as part of the raw material. In addition, in the treatment of Example 4, since the chemical was added to the clean treated water supply line, the chemical directly adhered to the thick plate of the product, but no problems such as dirt or corrosion occurred to the product. As is clear from the above results, it was confirmed that by the wastewater treatment method of the present invention, the oil concentration and suspended solid concentration of the treated water were sufficiently reduced, enabling compliance with wastewater regulations and water reuse. And since the oil content rate (%) of the sediment sludge could also be reduced to a sufficiently low level, it was confirmed that the obtained sediment sludge was recyclable as part of the raw material.

Explanation of Signs

[0050] 1 Continuous casting apparatus 2 Scale through - hole 3 Scale pit 4 Cross - flow sedimentation basin 5 Filter 6 Cooling tower 7 Rolling equipment

Claims

1. A wastewater treatment method for reducing the oil concentration and suspended solids concentration in wastewater containing oil and suspended solids, or oil and suspended solids and oil-combined suspended solids, in a direct cooling water system (however, carbon-based dust is not included as a treatment target) in a continuous casting facility or a rolling facility in the steel industry, comprising: The method includes an oil separation agent addition step of adding an oil separation agent so that the oil separation agent is contained in at least one of the steps of generating the oil and / or the suspended matter, and having the wastewater containing the oil and the suspended matter, or the oil and the suspended matter and the oil-combined suspended matter; The oil separating agent contains a nonionic polymer compound as an active ingredient, The process having the wastewater containing the oil and the suspended solids, or the oil and the suspended solids and the oil-bound suspended solids, is a scale sluice; The oil separating agent maintains the oil and the suspended solids in a separated state in the wastewater. A wastewater treatment method comprising the steps of:

2. The oil separation agent addition step is a step of adding an oil separation agent to at least one of the supply water to be supplied to a step in which the oil and / or the suspended matter are generated, the supply water to be supplied to a step having the oil and the suspended matter, or the oil and the suspended matter, and the wastewater containing the oil and the suspended matter and the oil-bound suspended matter; 2. The wastewater treatment method according to claim 1, wherein the supply water has an oil concentration of 5 ppm or less and a suspended solids concentration of 20 ppm or less.

3. 3. The method for treating wastewater according to claim 1 or 2, which is used to reuse oil and / or suspended solids separated from the wastewater.

4. A method for treating wastewater, comprising using treated water obtained from the method for treating wastewater according to claim 2 or 3 as feed water.

5. 3. The wastewater treatment method according to claim 1 or 2, wherein the nonionic polymer compound is a homopolymer, copolymer or terpolymer containing at least one monomer selected from the group consisting of acrylamide, ethylene oxide, propylene oxide, methyl vinyl ether, vinyl alcohol and vinyl acetamide as a constituent component.

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